This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-295367, filed Sep. 27, 2001; and No. 2002-94149, filed Mar. 29, 2002, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
In accordance with miniaturization of the silicon semiconductor integrated circuit, the size of an MIS (Metal Insulator Semiconductor) transistor is rendered smaller and smaller. According to ITRS (International Technology Road map for Semiconductors), 2000 edition, the technology nodes of 60 nm require EOT (Equivalent Oxide Thickness), which is a thickness of the gate insulator converted into the thickness of a silicon oxide film based on the dielectric constant, falling within a range of between 0.8 nm and 1.2 nm. However, if EOT is set to fall within the range noted above and a silicon oxide film or a silicon oxynitride film is used as a gate insulator, it is impossible to suppress sufficiently the leak current. Therefore, it is necessary to use an insulating film with a high dielectric constant, i.e., a high-k film containing metal, as the gate insulator.
In recent years, vigorous research has been conducted on, for example, Ta2O5, TiO2, Al2O3, ZrO2, HfO2, Zr silicate (ZrSiOx) and Hf silicate (HfSiOx) as a material of the next generation gate insulator with a high dielectric constant. Particularly, ZrO2, HfO2 and silicates thereof are high in the thermodynamic stability on an Si substrate, have a high dielectric constant and a large band gap and, thus, are considered to be particularly hopeful as a material of the gate insulator of the sub-1 nm generation.
However, the following problems are pointed out in respect of the thermal stability in the interface between the ternary insulator such as Mxe2x80x94Sixe2x80x94O (M=Zr, Hf) and the Si substrate.
The first problem is derived from the situation that oxidizing species such as O2 and H2O have a relatively high diffusion rate within the particular insulator. If the oxidizing species have a high diffusion rate within the insulating film, traces of the oxidizing species contained in the atmosphere are readily migrated through the insulating film during various heat treatment steps, with the result that a thick SiO2 film is formed at the interface between the insulator and the Si substrate. The formation of the SiO2 film lowers the dielectric constant of the gate insulator so as to increase EOT.
The second problem is brought about in the case where the partial pressure of the oxidizing species within the heat treating atmosphere is lowered in an attempt to prevent the SiO2 film from being formed. Specifically, if the structure of an insulating film/Si substrate is subjected to a heat treatment at a temperature not lower than 900xc2x0 C. under UHV (Ultra High Vacuum) in which the partial pressure of the oxidizing species is lowered, it has been confirmed that a metal silicide (MSix) is produced at the interface between the high-k film and the Si substrate, which brings about degradation of the morphology. Incidentally, the particular reaction takes place not only at the interface between the high-k film and the Si substrate but also at the interface between the high-k film and a polycrystalline silicon (poly-Si) gate electrode or a polycrystalline silicon germanium (poly-SiGe) gate electrode.
As described above, in order to suppress the formation of an SiO2 film at the interface between the high-k film and the Si substrate, it is necessary to suppress the partial pressure of the oxidizing species to a low level in the atmosphere. However, if the partial pressure of the oxidizing species is excessively lowered, a silicide is formed. Therefore, in the case where an Si substrate having a high-k film formed thereon is subjected to a heat treatment step, it is necessary to control the partial pressure of the oxidizing species in the atmosphere to fall within a prescribed range in order to suppress both formation of an SiO2 film and silicide.
However, the partial pressure range of the oxidizing species in which formation of an SiO2 film and a silicide can be suppressed is very narrow, which makes it very difficult to control the partial pressure of the oxidizing species to fall within the desired range. This raises a serious obstacle in applying a high-k film to the present semiconductor process, which includes many heat treatment steps at high temperatures such as an activation anneal.
According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising forming a structure including a first layer containing Si and a metal oxide layer in contact with the first layer, the metal oxide layer being higher in dielectric constant than silicon oxide, and heating the structure in an atmosphere containing He and/or Ne.
According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising forming a structure including a first layer containing Si and a metal oxide layer in contact with the first layer, the metal oxide layer being higher in dielectric constant than silicon oxide and at least one of the first layer and the metal oxide layer containing He and/or Ne, and heating the structure.
According to a third aspect of the present invention, there is provided a semiconductor device, comprising a first layer containing Si, and a metal oxide layer in contact with the first layer, the metal oxide layer being higher in dielectric constant than silicon oxide, and at least one of the first layer and the metal oxide layer containing He and/or Ne.
In each of the first and second aspects of the present invention, it is possible for the particular structure to further comprise a second layer. Also, the device according to the third aspect of the present invention may further comprise a second layer.
In each of the first to third aspects of the present invention, it is possible for the metal oxide layer to be a gate insulator. It is possible for the first layer to include at least one of an Si underlying layer, a gate electrode and a sidewall insulating film. Also, it is possible for the particular structure or the device to further comprise as the second layer at least one of, for example, an Si underlying layer, a gate electrode and a sidewall insulating film.
It is possible for the Si underlying layer to be, for example, an Si substrate or an Si substrate of an SOI substrate. It is possible for that surface of the Si underlying layer which faces the metal oxide layer to be oxidized. In other words, it is possible for the Si underlying layer to comprise a silicon oxide film formed on the surface thereof that faces the metal oxide layer.
It is possible for the first layer to be, for example, an Si layer or an SiGe layer. Alternatively, it is possible for the first layer to be an insulating layer containing Si such as a silicon oxide layer or a silicon oxynitride layer.
Similarly, it is possible for the second layer to be, for example, an Si layer or an SiGe layer. Alternatively, it is possible for the second layer to be an insulating layer containing Si such as a silicon oxide layer or a silicon oxynitride layer.
The metal oxide layer has a dielectric constant higher than that of silicon oxide. It is possible to use a metal oxide, a metal oxynitride or a silicate containing a metal, Si and oxygen as the material of the metal oxide layer satisfying the particular requirement. The material that can be used for forming the metal oxide layer includes, for example, ZrO2, HfO2, BeO, MgO, SrO, BaO, Y2O3, CeO2, PrxOy, Nd2O3, ThO2, RuO2, IrO2, Al2O3, In2O3, ZrON, HfON, ZrSiOx, HfSiOx, ZrSiOxN, and HfSiOxN. It is possible for the metal oxide layer to be made of a single or a plurality of materials. Also, it is possible for the metal oxide layer to be of a single or multi-layered structure.
In the first aspect of the present invention, it is possible for the heat treatment of the structure to comprise heat treating the structure in the atmosphere at an absolute temperature T of 650xc2x0 C. or higher. In this case, it is possible for the sum of the partial oxygen and water vapor pressures in the atmosphere, to be 133xc3x971011.703-18114/T Pa or lower. Alternatively, it is possible for this pressure to be 133xc3x97108.903-18114/T Pa or lower.
In the first and second aspects of the present invention, it is possible for the formation of the structure to comprise forming a metal oxide layer on an Si underlying layer and depositing Si or SiGe on the metal oxide layer by a chemical vapor deposition using a silane gas as at least a part of a raw material gas so as to form the first layer. In this case, it is possible for the chemical vapor deposition to comprise depositing Si or SiGe on the metal oxide layer with the temperature of the Si underlying layer set lower than 600xc2x0 C., and further depositing Si or SiGe on the metal oxide layer by elevating the temperature of the Si underlying layer to 600xc2x0 C. or higher.
It is possible for the method according to each of the first and second aspects of the present invention to further comprise patterning the first layer and the metal oxide layer before heating the particular structure so as to form a gate electrode and a gate insulator, respectively.
It is also possible for the method according to each of the first and second aspects of the present invention to further comprise oxidizing the surface of at least one of the first and the second layers by using an oxidizing atmosphere containing He and/or Ne before heating the particular structure.
In each of the first and second aspects of the present invention, it is possible for at least one of the first layer, the second layer and the metal oxide layer to contain He and/or Ne.
It is also possible for the method according to each of the first and second aspects of the present invention to further comprise supplying at least one of the first layer, the second layer and the metal oxide layer with He and/or Ne.
In the second aspect of the present invention, it is possible for the heating of the particular structure to be carried out in an atmosphere containing He and/or Ne.
Further, in each of the first and second aspects of the present invention, it is possible for every heat treatments that is carried out at a temperature of 650xc2x0 C. or higher after forming the particular structure to be carried out in an atmosphere containing He and/or Ne.